Fuze

ABSTRACT

An ordnance fuse is provided for distinguishing interposed material, such as a forest canopy, from a true target; providing a firing signal at the latter and refraining from firing at the former. An electronic integrating comparator compares the time interval of contact with a target or canopy with a selected time interval and provides a firing signal when the contact time exceeds a threshold that distinguishes a true target from intervening material.

[451 Apr. 23, 1974 United States Patent [191 Cummings l02/70.2 l02/70.2X

[54] FUZE 3,327,631 6/1967 Howard at al. [75] inventor: Jerry W. CummiPalos Verdes ,211 l|/19 6 Wlnston.........................

Estates, Calif.

Primary ExaminerSamuel W. Engle [73] Assignee: Rockwell InternationalCorporation, Assistant E i Th H, W bb El q Calif- Attorney, Agent, orFirmR. D. Seibel Aug. 21, 1967 Appl. No.: 663,472

[22] Filed:

[57] ABSTRACT An ordnance fuse is provided for distinguishing inter-[52] U s C! 102/70 2 R 320 posed material, such as a forest canopy, froma true 15/40 i 11/02 target; providing a firing signal at the latter andrefraining from firing at the former. An electronic inte- [5l] Int.CL... [58] Field of Search......................... lO2/70.2; 320/1grating comparator compares the time interval of contact with a targetor canopy with a selected time interval and provides a firing signalwhen the contact [56] References Cited UNITED STATES PATENTS timeexceeds a threshold that distinguishes a true target from interveningmaterial.

l02/7O 2 X 307/885 102/70 2 X 8 Claims, 6 Drawing Figures PATENTEDAPR 23 m4 SHEET 1 BF 2 TIMER DETONATOR FIRING COMMAND FIG. I

SENSOR COMPARATOR H2 ARMING SWITCH INVENTOR.

JERRY W. CUMMINGS BY W (QM FIG. 2

ATTORNEY ATENTEDAPR 23 19m 8 5; 7 03 SHEET 2 UF 2 VII/Ill 46 DETONATORINVENTOR. 6 JERRY w. CUMMINGS ATTORNEY FUZE BACKGROUND In the selectionof fuses for ordnance devices such as aerial bombs, rockets andartillery shells it is significant that the fuse be operable inconditions that anticipate the characteristics of potential targets ofthe weapon. Thus, for example, a weapon employed against concrete wouldemploy a fuse different from one intended to impact on water. Four broadclasses of fuses are employed in ordnance devices, viz., (l) fuses whichdepend upon deceleration sensing upon impact to cause detonation, (2)fuses which depend on structural deformation or mechanical displacementof elements during impact for detonation, (3) fuses which depend onsensing of target proximity by electromagnetic radiation for detonation,and (4) detonation after a selected time interval following some event.

A difficulty in the practical application of fuses arises when materialsare interposed between the first entry of the weapon into the targetvicinity and a point some distance further along the trajectory at whichdetonation would be most effective. Such a condition exists, forexample, in the penetration of buildings, in which case detonation of abomb near the foundation causes greater destruction than detonation atthe roof. A similar practical example of this type is in the use ofantipersonnel weapons against targets located below a screening layer ofbranches and the like, referred to hereinafter as canopy.

The problem of canopy discrimination is of particular concern in jungleenvironments where a heavy growth occurs at various heights above theground. This is the type of growth one observes by looking upward towardthe sky from a forest floor. A canopy is made up of many canopy elementssuch as branches of various thicknesses and lengths, leaves, vines, andother material. In any given forest the density of canopy elements maybe uniformly distributed above the ground or they may be confined to oneor more layers of varying thicknesses which are separated by spaces inwhich there are no canopy elements. It is also found that clearings andthe like occur wherein no canopy elements whatsoever are involved. Theground beneath such a canopy is often swampy terrain or comprises a deeplayer of rotting vegetation, both of which are generally soft andpenetrable in nature. Because of this, relatively sensitive fuses arerequired for sensing impact with soft ground.

In a situation where penetration of interposed materials, such as truckor building roofs or forest canopy, is involved, the previouslyavailable types of fuses have not been completely satisfactory. Fusessensing deceleration or relying on structural deformation are notcompletely satisfactory since, if the elements are strong orinsensitive, functioning of the fuse at ground level may not occur insoft earth, mud, or water such as is often found beneath forest canopy.Similarly, if the fuses are very sensitive, in order to function uponimpact with mud or water, they are also sufficiently sensitive to beactuated by the interposed material.

Electromagnetic sensing devices have not been developed,fordiscriminating between inter-posed material and target areas.

Attempts to introduce discrimination against interposed material havebeen employed in which the fusing device provides a selected time delaybetween first activation and subsequent detonation of the weapon. Thus,for example, a sensitive fuse is activated on contact with canopy anddetonation occurs a short time later to allow time to fall closer to theground. Delayed discrimination is unsatisfactory where the target iscompletely clear of interposed material, or when the height of theinterposed material and the desired detonation point is variable. When atime delay is employed and there is no interposed material the weaponmay be destroyed by impact before functioning of the detonator; or theweapon may tunnel deep into the ground before detonation which may notbe the desired mode of operation. Variations in the velocity of theweapon near impact which are a necessary consequence of tacticaldelivery situations also make simple time delay discriminationsimpractical in many situations.

Another significant safety consideration in many ordnance fuses is aprovision for arming the weapon only after it has separated asubstantial distance from the launching system such as a rocket tube,gun barrel, or airplane.

It is also often desirable from the standpoint of security of weapontechnology from analysis of duds by the enemy to provide in the fuse,means to separately detonate the weapon in the circumstance where acommitted round is for some reason not detonated by the regular fusingarrangement. Such provisions are conventionally known as sanitizationand may include simple time delays or auxiliary mechanisms which respondto attempts of enemy personnel to dismantle the round for examination ofits construction.

SUMMARY OF THE INVENTION Thus there is provided in the practice of thisinvention according to a preferred embodiment an ordnance fuse capableof discriminating between interposed material and a target area withdetonation at the latter. In a preferred embodiment discrimination isobtained by comparing the elapsed time of presence of the interposedmaterial and preventing detonation when the elapsed time is less than athreshold and providing detonation when the elapsed time exceeds athreshold.

Objects and many of the attendent advantages of this invention will bereadily appreciated as the same becomes better understood by referenceto the following detailed description, when considered in connectionwith the accompanying drawings wherein:

FIG. I comprises a block diagram of a fuse incorporating the principlesof this invention;

FIG. 2 is a circuit diagram of an embodiment of the fuse of FIG. 1;

FIG. 3 is a switch preferred for use in the fuse of FIG.

FIG. 4 comprises a detailed view of a portion of the switch of FIG. 3;

FIG. 5 comprises another embodiment of sensor useful in the fuse of FIG.1; and

FIG. 6 comprises a circuit diagram of another embodiment of the fuse ofFIG. 1.

Throughout the drawings like numerals refer to like parts.

The description hereinafter is particularly directed to discriminationagainst canopies as often found in forests. It will be apparent that thedescriptions are equally applicable to other kinds of interposedmaterial such as man-made barricades, building structures, fabrics,

camouflage structures. truck and van roofs, and a wide variety ofsimilar structures. It will also be apparent upon review of thedescription that the principles are also applicable to bombs designed totunnel into the ground and a fuse can readily be provided which willcause detonation when such a bomb enters a void space in the earth, suchas a man-made tunnel, thereby greatly enhancing the destructive effects.

As discussed herein the fuse is regarded as an element of a fallingaerial bomb delivered against a soft target in a swampy jungle. It willbe apparent to one skilled in the art that many other applications ofsuch a fuse are of utility in other weapons and practical situations.

Reference is also made throughout to detonation of the weapon, however,it will be apparent to one skilled in the art that detonation is not theonly yield of a weapon in practical situations and conflagration orsmoke marking and other types of weapon yield may be involved in certainsituations.

The passage ofa bomb through a canopy can be considered in terms of aseries of mechanical impulses to the bomb due to impact with variouselements of the canopy and ultimately the ground. It is found that thetime that a falling bomb is in contact with a limb or other canopyelement is relatively short compared with the time between when the bombstrikes the ground and destruction thereof due to the effects of extremedeceleration. Thus, for example, it is found that for a limb about 6inches in diameter and a bomb velocity of about 300 feet per second, acontact duration of only about 1.6 milliseconds results. Where thevelocity of the falling bomb is about 1,000 feet per second, the contactduration is reduced to about 0.5 milliseconds. This order of magnitudeof contact duration is increased in the event the limb deflects underimpact and will obviously vary with other size, strength, and inertialcharacteristics of the canopy. It will also be apparent that the maximumtime of contact will be realized only in the instance ofa square hit andthat glancing directions of impact will result in shorter impactdurations. It will also be apparent that when numerous canopy elementsare involved that the sum of the time intervals of contact withsuccessive elements may increase appreciably. Since the force involvedin an impact with a canopy element is dependent on size and inertialcharacteristics of the element, a threshold is readily provided fordisregarding small forces such as encountered with leaves or twigsalone.

Thus a preferred embodiment discrimination of canopy is made bycomparing a time interval of contact with canopy elements with aselected reference time interval.

FIG. 1 illustrates in block diagram form a fuse incorporating theprinciples of this invention. As illustrated therein there is providedan arming switch 10 which may comprise any of many conventionalswitches, operated by springs, lanyards and the like for initiating thefunctional mode of the weapon so that it is armed and ready fordetonation upon reaching a target. If desired, a time interval can beemployed in the arming switch with the function of delaying the armingto provide safety for the launching system. The arming switch 10activates a timer 11 and a comparator 12. The timer 11 may comprise aconventional electronic, mechanical, electromechanical or chemical timerfor providing a detonation signal after an elapsed time interval afterarming. This interval is longer than the delivery time of the weapon andprovides sanitization in case the weapon is not detonated by the primaryfusing system. A time interval of from 500 to 1,000 seconds isconveniently employed in many applications for destroying duds.

A sensor 13 is provided for detecting occurrence of impulse conditionscharacteristic of impact with elements of a forest canopy and also theground beneath. Thus the sensor 13 detects entry of the fuse into acanopy and exit therefrom. The sensor may comprise means for detectingimpact of the weapon with canopy elements or means for sensing theproximity of the elements to the weapon.

The sensor 13 provides a momentary signal during occurrence ofacondition to be sensed, such as, for example, contact between the weaponand a canopy element. The signal ends when the condition ends. Thissignal is applied to the comparator 12 where it is compared with apreselected time interval which provides a threshold for actuation ofthe fuse. If the time duration of the signal from the sensor is lessthan the threshold interval there is no actuation of the fuse. If,however, the time interval is longer than the selected threshold, asignal is applied from the comparator 12 through an OR gate 14 to afiring command element 15 which provides firing power to a conventionaldetonator 16 for detonation of the weapon. If, for some reason, thecomparator does not apply a signal longer than the threshold to the ORgate, such a signal is eventually applied by the timer 11 at the endofits cycle and detonation is thereby caused.

FIG. 2 comprises a circuit diagram of a specific embodiment of the fuseof FIG. 1. Superimposed on the circuit diagram by dashed lines andidentified by the same reference numerals, are the block elementsillustrated in FIG. 1. Thus, there is provided in a preferred embodimentas illustrated in FIG. 2 an arming switch 10 which preferably comprisesa double pole switch for operably connecting two batteries 18 and 19 tothe electronic circuitry of the fuse. The battery 18 provides a voltageof proper level for operating the electronic elements of the fuse andthe battery 19 provides additional energy as may be required foroperating the detonator 16. It will be apparent to one skilled in theart that by proper selection of electronic circuit elements that asingle battery can be employed if desired.

In order to provide energy for detonation the batteries 18 and 19 areemployed for charging a firing capacitor 21 to a sufficient energy levelfor operating the detonator 16. The firing capacitor 21 serves to storeenergy and provide a heavier current upon command across the detonator16 than may be available from the batteries alone. A high value leakageresistor 22 is provided across the capacitor 21 for safety reasons. Theleakage resistor 22 slowly drains the capacitor 21 so that if thecircuit is for some reason accidentally activated and inactivated thecharge drains off of the capacitor and renders the fuse safe again. Theleakage resistor also serves to bias a silicon controlled rectifier 39,hereinafter described, that operates as a switch to discharge thecapacitor 21 upon receipt of an appropriate signal.

A safety resistor 23 is also provided in the arming circuit between thebattery 19 and the capacitor 21 so that a time delay occurs afterclosing the arming switch 10 and before a sufficient energy level hasbuilt up in the capacitor 21 to initiate the detonator 16. A very fewseconds delay is sufficient for protection of launching aircraft. Itwill be apparent that the safety resistor 23 can be deleted from thecircuit and delay means associated with the arming switch to provideclosure thereof at a selected time interval after launching the bombfrom an aircraft.

As mentioned hereinabove upon closure of the arming switch 10 a timer 11and a comparator 12 are activated. The timer 11 preferably comprises aconventional linear charging circuit which permits accurate presettingof time intervals of fairly long duration, such as from 5 to 15 minutes.In a preferred embodiment the linear timing circuit comprises acapacitor which is charged by the battery 18 through a resistor 26 andan NPN transistor 27. In order to linearize the charging rate on thecapacitor 25 the voltage thereon is applied as bias to the base of anNPN transistor 28 which conducts correspondingly through a resistor 29.The voltage across the resistor 29 is applied as bias to the base of thetransistor 27 for controlling the current therethrough for charging thecapacitor 25. In this manner a more linear charging rate of thecapacitor 25 is obtained. It will be apparent to one skilled in the artthat other types of charging circuits or timers can be provided. .Thecomparator 12 is also activated upon closure of the arming switch 10,however, nothing actually occurs in the comparator until such time asthe sensor 13 is actuated or until the timer 1 1 effects operation. In apreferred embodiment the sensor comprises a momentary switch ashereinafter described, which is normally open and is closed only duringcontact with an object such as forest canopy or the ground. Upon closingof the switch 13 a detonating cycle is initiated wherein current flowsthrough a resistor 31 for charging a capacitor 32. It will be apparentthat the rate of charging of the capacitor32 is dependent on the valueof the resistor 31 and capacitor 32, therefore it is desirable incertain instances to employ a variable resistor 31 as illustrated inFIG. 2 for controlling rate of charge of the capacitor and hence thetime required to reach a selected voltage level. Variation of thecharging time to give a detonating cycle in the range of from one to tenmilliseconds is readily provided. If desired, fixed values can beemployed or a variable capacitor can be used in lieu of a variableresistor. The voltage on the capacitor 25 on the timer and the voltageon the capacitor 32 in the comparator are both applied to the OR gate 14which comprises a pair of diodes 33 arranged so that the higher of thetwo voltages is applied to a unijunction transistor 34.

,The unijunction transistor 34 is reverse biased by resistors 36 and 37so that no current flows from the OR gate until a sufficient voltage isapplied to the unijunction transistor to forward bias it. As mentionedhereinabove the voltage from the capacitor 25 is applied to theunijunction transistor and the voltage on the capacitor 32 is alsoapplied to the unijunction transistor. When either of these voltagesexceeds the reverse biasing voltage the unijunction transistor fires,thereby producing a substantial current flow and a voltage spike in theR-C network 36, 37 and 38 which can be considered a detonating signal.The voltage spike is also applied to a silicon controlled rectifier 39which is thereby swung to a conducting state. The silicon controlledrectifier 39 is normally biased in a nonconductive state by resistors 22and 23. When the silicon controlled rectifier 39 becomes conductive acircuit through detonator 16 is completed. A heavy current flows fromthe capacitor 21 which has been charged through resistor 23 from battery19. This current flows through the detonator 16 and the conductingsilicon controlled rectifier 39.

It will be apparent that if no firing signal occurs from the sensorcapacitor 32 the voltage on the capacitor 25 in the timer 1 1 will,after a preselected time interval, be sufficient to fire the unijunctiontransistor 34 and thereby detonate the aerial bomb in the same manner.In the usual situation, however, signal from the capacitor 32 causesdetonation of the bomb.

In the embodiment of FIG. 2 the unijunction transistor 34 of thecomparator 12 is also used with the timer circuit 11 via the OR gate 14for providing a firing signal. Thus a portion of the comparator isemployed in conjunction with elements of the timer. From one point ofview, the unijunction transistor 34, with its bias resistors, can beconsidered a comparator and the resistor 31 and capacitor 32 considereda sensor-timer for providing a voltage signal to the comparator which isa function of the time the sensor switch 13 is closed.

As hereinabove mentioned, closing of the contact switch 13 charges thecapacitor 32 through the resistor 31 at a selected rate. If the switch13 remains closed for a time longer than the selected threshold thedetonating cycle is completed and capacitor 32 is charged to asufficient voltage level to fire the unijunction transistor. Thus, forexample, if an aerial bomb strikes an element of a canopy the switch 13is momentarily closed but reopens immediately upon breaking contact withthe canopy element. If the time of contact is less than the thresholdvalue no detonation of the bomb occurs. If, however, the bomb strikesthe ground the contact switch 13 is kept closed and when the thresholdtime is exceeded the charge on the capacitor 32 builds to a level forfiring the unijunction transistor and detonating the bomb.

It will be apparent that if the contact switch 13 is closed severaltimes in rapid succession for an integrated time greater than thethreshold, the detonating cycle is effectively completed and thecapacitor 32 is charged to a sufficient voltage for detonating theweapon. If desired, therefore, a high value resistor 41 can be providedacross the capacitor 32 to discharge the capacitor and practicallyeliminate the low frequency integration inherent therein such as whentime intervals are present between intermittant closures of the contactswitch 13. If this resistor is employed the capacitor 32 charges to thefiring voltage only if the switch is continuously closed for a period inexcess of the reference time, as by ground contact or is intermittantlyclosed at a high frequency for an integrated time greater than thethreshold, allowing for the leakage occurring in the integrated timeinterval. It will be apparent to one skilled in the art that thedescribed circuitry and duals and analogs thereof are readily adaptableto advanced miniaturization techniques thereby permitting use inrelatively small tactical weapons.

A typical switch useful in the practice of this invention for contactwith canopy elements, ground, and the like, is illustrated in FIGS. 3and 4. As illustrated therein, there is provided a base plate 42 or thelike forming the nose or leading end of a fin stabilized aerial bomb,the end of which is shown in phantom in FIG. 3.

On the base plate 42 is mounted an inner saucer-like plastic member 44,and concentric therewith an outer saucer-like plastic member 45. Each ofthe plastic members 44 and 45 comprises a dished sheet of glass fabricimpregnated with an epoxy resin which for a four inch diameter switchmember is preferably about onesixteenth inch thick and the members arepreferably spaced apart about one-half inch. Each of the plastic membersis metallized on one side to provide an electrically continuous layer.An enlarged section of the dishlike members 44 and 45 is illustrated inFIG. 4. The outer member 45 comprises a plastic sheet 46 with a metallayer 47 on the concave side thereof, such as may be provided by vacuumdeposition, electroless plating, or the like. The saucer-like member 44is similar with the metal layer 69 on the concave side of a plasticsheet 68 so as to be adjacent the metal layer 47 on the saucer-likeelement 45.

Referring again to FIG. 3 an electrical contact 48 is made to the metal69 layer on the outside of the saucerlike element 44. Similarly anelectrical contact 49 is made to the metal layer 47 on the inside of thesaucerlike member 45. Thus the saucer-like members 44 and 45 haveelectrically conductive metal layers facing each other and form acontact sensor 13. The electrical connections 48 and 49 are connected tothe electronic circuit hereinabove described in relation to FIG. 2 asleads to the sensor 13.

Upon contact of the aerial bomb 43 with a canopy element or the ground,the outer saucer-like member 45 is mechanically deformed so as to bringits metal layer in electrical contact with the metal layer on the innersaucer-like member 44 which may also elastically deform. Thesecontacting metal layers serve as a switch. If bomb contact is made witha canopy element and said contact is broken in a short time, thesaucerlike plastic elements 44 and 45 elastically spring back to theiroriginal position and electrical contact therebetween is broken, therebyopening the switch. Thus the saucer-like elements 44 and 45 form amomentary switch which is closed only during mechanical deformation ofthe elements. Upon striking the ground, or the like, the saucer-likeelements are deformed into contact and remain in contact, therebymaintaining the switch closed for a time longer than the threshold andpermitting the detonating cycle to go to completion.

It is found in building such a switch that glass fabric reinforced epoxyresin about one-sixteenth inch thick is sufficient to provide resiliencyfor re-opening the switch and sufficient strength and impact resistanceto avoid cracking and destruction of the plastic upon impact. Theplastic members are also sufficiently strong to avoid switch closingupon contact with minor canopy elements such as leaves, twigs, and thelike. The described switch is sufficiently sensitive to close and remainclosed upon contact with water or soft soil. It is desirable in apractical weapon to provide reliability by having several parallel andredundant electrical contacts 48 and 49 with the metal layers on thesaucerlike elements so that inadvertent cracking or damage to the metallayer will not render the switch inoperable. If desired, the base plate42 can be provided as concentric conductive and non-conductive rings sothat electrical contact is made around the entire periphery of thesaucer-like elements 44 and 45.

It will be apparent that the thickness, material and spacing of theplastic members can be varied as desired to obtain a selected closingforce for operating the switch. The physical characteristics are thusselected according to the impact velocity of the weapon and the natureof canopy material it is expected to encounter. A significant factor isthat the switch operating sensitivity or sensory threshold is separatelyand independently variable from the time threshold in the detonatingcycle. An easily operated switch may be employed with a long timethreshold in some tactical situations and a relatively insensitiveswitch with a short time threshold may be desirable under otherconditions. Thus two discrimination thresholds are present in the fuse,one dependent on the magnitude of a sensory input such as contact withan element, and the other a time discrimination dependent on thepresence or absence of a condition greater in magnitude than theselected sensory input threshold.

If the sensory input is selected as contact with an element it will alsobe apparent that discrimination can readily be obtained with othercontact switch arrangements. It is significant that the switch indicatethe presence or absence of contact above the threshold and this can beprovided with springs and inertial masses, gas filled chambers, andother types of elastically resilient switches well known to thoseskilled in the art.

Another type of sensor 13 useful in the practice of this invention isillustrated in FIG. 5. This sensor comprises a light source 50 which isfocused by a lens 51 to a point immediately outside a window 52 at theleading edge of a bomb. Light passing through the window 52 striking acanopy element 53 or the like (or the ground) is reflected back throughthe window so as to be focused on a photodetector 54 by a lens 55. Inthe absence of any solid material immediately outside the window nolight is reflected to the photodetector and this sensor remains open.When, however, an element of canopy material or the ground is outsidethe window in immediate proximity thereto, light is reflected to thephotodetector and the sensor is momentarily closed so long as thematerial remains in front of the window. Such a sensor is more sensitiveto minor canopy elements than the mechanical switch and may be desirablein some situations. A discrimination threshold can be provided based onthe reflectivity of the material outside the window or the distance fromthe window to the object or some aspect of the spectral signature of anexpected target.

It will be apparent that in lieu of or in addition to the mechanicallyoperated switch and the light reflection switch hereinabove describedthat other types of switching arrangements such as an integratingaccelerometer or the like can be employed with a canopy discriminatingfuse of the type described herein. It should also be appreciated thatvarious combinations of sensors functioning as switches of typessensitive to different conditions characteristic of canopy and groundcan be employed in different logic arrangements such as AND, OR, or NORso that the detonator is tired in the alternative or when more than oneswitch is closed in order to provide greater discrimination between atrue target and canopy elements or other false indicators of a target.

An alternative embodiment of fuse incorporating the principles of thisinvention is illustrated in FIG. 6. As illustrated therein an armingswitch 'activates a timer 11, a threshold comparator 112, and also afiring command circuit 115. The timer 111 may comprise a simple R-Ccircuit for charging a capacitor 57 after the arming switch 110 isclosed. Although this is not a linear charging circuit as provided inthe preferred embodiment a sufficiently accurate timing interval forsome purposes can be achieved. When the timing circuit has charged thecapacitor 57 to a sufficient voltage level, a glow discharge or gasfilled tube 58 connected across the capacitor 57 is fired therebyproviding a pulse of light. Such a simple circuit is often known as arelaxation oscillator and a wide range of time constants can readily beprovided. It is preferred to have a time constant of several hundredseconds. If desired, instead of the light pulse, the current, and hencevoltage, pulse when the tube fires can be employed in a detonationcycle.

The comparator circuit 112 also comprises a short time constantrelaxation oscillator including a capacitor 59, however, this circuitalso contains a sensor 113 which in a preferred embodiment comprises anormally open, momentarily closable switch. As in the preferredembodiment closing of the switch 113 for a time greater than a selectedthreshold permits the charge on the capacitor 59 to build to a voltagevalue that is sufficient for firing a glow discharge tube 60 connectedthereacross, thereby providing a pulse of light. The threshold voltageof the glow discharge tube provides the voltage comparison for asensor-timer RC circuit if one prefers to consider the circuit in thatnomenclature.

Upon closing of the arming switch 110 a battery 64 charges a capacitor65 in the firing command circuit 115 to an energy level sufficient forfiring a detonator 116.

Either the pulse of light from the timer glow tube 58 or from thecomparator glow tube 60 may impinge on a photo-transistor 61 in thefiring command circuit 115. The photo-transistor 61 is biased byresistors 62 and 63 so as to be turned off in the absence of lightimpinging thereon. When light from either the timer 111 or thecomparator 112 impinges on the phototransistor 61 it becomes conductiveand the charge on the capacitor 65 is discharged through thephoto-transistor and the detonator 116 thereby detonating the bomb. Thenet operation of an embodiment as illustrated in FIG. 6 is the same asin the preferred embodiment and there is the additional advantage thatthe electrical circuits are interconnected only by an optical path andsomewhat greater safety may be achieved. if desired, a single glow tubecan be employed and the two relaxation oscillators can both be connectedthereto by an electronic OR gate. It may also be desirable to provide anopaque shield in the optical path prior to arming of the fuse for safetypurposes.

In a fuse constructed according to the principles of this invention,values for the comparator were selected so that a threshold time of 1.4milliseconds was required for a firing command to be generated. It wasfound in repeated tests that a contact switch pulse duration of 1.2milliseconds consistently gave no firing command and a duration of 1.4milliseconds consistently generated a firing command. This time intervalis sufficiently short that, upon contact with the ground, structuraldeformation occurs in the contact switch and not in the body of thebomb. A short time is required so that the bomb is not damaged by impactforces before detonation for maximum effectivity.

It is to be understood that the above described embodiments are merelyillustrative of the application of the principles of this invention.Those skilled in the art may readily devise other variations that willembody the principles of the invention. It is therefore to be understoodthat within the scope of the appended claims the invention may bepracticed otherwise than is specifically described.

What is claimed is:

1. An improved fuze for an ordnance device comprismg:

a sensor for detecting contact between the ordnance device and a target,and between the ordnance device and a forest canopy, said sensorproviding a first signal upon contact with a target and a second signalupon contact with a forest canopy, said first and second signals beingidentical except as to duration;

a sensing circuit responsive to said first and second signals forproviding a firing signal to the ordnance device; and

a time integration circuit interposed between said sensor and saidsensing circuit for preventing a firing signal unless the duration ofsaid first signal or said second signal exceeds a selected timethreshold, said time threshold being greater than the time required forthe ordnance device to break contact with a forest canopy.

2. A fuze as defined in claim 1 wherein said sensor comprises a contactswitch biased to an open state and closable with a force exceeding athreshold value characteristic of both a target and a forest canopy.

3. A fuze as defined in claim 2 wherein the switch comprises: an outernon-conductive, elastic saucer-like member;

a conductive layer on the concave surface of the outer member;

an inner non-conductive, elastic saucer-like member spaced apart fromthe concave side of the outer member; and

a conductive layer on the convex surface of the inner member.

4. A fuze as defined in claim 2 wherein said sensing circuit and saidtime integration circuit collectively comprise:

a power supply;

a timing capacitor;

a resistor in series with said timing capacitor, said power supply, andsaid sensor so that a signal from said sensor causes charging of saidtiming capacitor at a selected rate;

a unijunction transistor connected to said timing capacitor and reversebiased for providing a current pulse when voltage on said timingcapacitor exceeds a threshold;

a storage capacitor;

means connected to said power supply for charging said storage capacitorat a selected rate;

a silicon controlled rectifier reverse biased to be non conducting;

a network for forward biasing said silicon controlled rectifier to beconductive in response to a current pulse from the unijunctiontransistor, said silicon controlled rectifier being connected to saidstorage capacitor for discharge thereof through an external circuit.

5. A fuze as defined in claim 1 wherein said sensor comprises:

a light source;

means for focusing light from the source a short distance from theordnance device; and

means for sensing light reflected from an object upon which the lightfalls.

6. A fuze for an ordnance device for discriminating a true target and aspurious indication of a target, and causing detonation of the ordnancedevice at the true target and preventing detonation at the spurioustarget comprising:

a contact switch resiliently biased to actuate upon application of aforce greater than a threshold value and to deactivate upon release offorce to less than the threshold value;

a time integration circuit operable only in response to switchactuation, said circuit providing a firing signal when the elapsed timeof switch actuation exceeds a threshold time.

7. A fuze as defined in claim 6 wherein said time integration circuitcomprises:

a power supply;

a timing capacitor;

a resistor in series with said timing capacitor, said power supply, andsaid sensor so that a signal from said sensor causes charging of saidtiming capacitor at a selected rate;

a unijunction transistor connected to said timing capacitor and reversebiased for providing a current pulse when voltage on said timingcapacitor exceeds a threshold;

a storage capacitor;

means connected to said power supply for charging said storage capacitorat a selected rate;

a silicon controlled rectifier reverse biased to be nonconducting;

a network for forward biasing said silicon controlled rectifier to beconductive in response to a current pulse from the unijunctiontransistor, said silicon controlled rectifier being connected to saidstorage capacitor for discharge thereof through an external circuit.

8. A method of distinguishing a true target such as the ground and aspurious target such as a forest canopy in an ordnance fuze comprising:

sensing a contact between the ordnance fuze and an object when thecontact force exceeds a threshold value;

commencing a firing cycle when the contact is sensed;

interrupting the firing cycle when the contact is broken; and

providing a firing signal when the duration of contact

1. An improved fuze for an ordnance device comprising: a sensor fordetecting contact between the ordnance device and a target, and betweenthe ordnance device and a forest canopy, said sensor providing a firstsignal upon contact with a target and a second signal upon contact witha forest canopy, said first and second signals being identical except asto duration; a sensing circuit responsive to said first and secondsignals for providing a firing signal to the ordnance device; and a timeintegration circuit interposed between said sensor and said sensingcircuit for preventing a firing signal unless the duration of said firstsignal or said second signal exceeds a selected time threshold, saidtime threshold being greater than the time required for the ordnancedevice to break contact with a forest canopy.
 2. A fuze as defined inclaim 1 wherein said sensor comprises a contact switch biased to an openstate and closable with a force exceeding a threshold valuecharacteristic of both a target and a forest canopy.
 3. A fuze asdefined in claim 2 wherein the switch comprises: an outernon-conductive, elastic saucer-like member; a conductive layer on theconcave surface of the outer member; an inner non-conductive, elasticsaucer-like member spaced apart from the concave side of the outermember; and a conductive layer on the convex surface of the innermember.
 4. A fuze as defined in claim 2 wherein said sensing circuit andsaid time integration circuit collectively comprise: a power supply; atiming capacitor; a resistor in series with said timing capacitor, saidpower supply, and said sensor so that a signal from said sensor causescharging of said timing capacitor at a selected rate; a unijunctiontransistor connected to said timing capacitor and reverse biased forproviding a current pulse when voltage on said timing capacitor exceedsa threshold; a storage capacitor; means connected to said power supplyfor charging said storage capacitor at a selected rate; a siliconcontrolled rectifier reverse biased to be nonconducting; a network forforward biasing said silicon controlled rectifier to be conductive inresponse to a current pulse from the unijunction transistor, saidsilicon controlled rectifier being connected to said storage capacitorfor discharge thereof through an external circuit.
 5. A fuze as definedin claim 1 wherein said sensor comprises: a light source; means forfocusing light from the source a short distance from the ordnancedevice; and means for sensing light reflected from an object upon whichthe light falls.
 6. A fuze for an ordnance device for discriminating atrue target and a spurious indication of a target, and causingdetonation of the ordnance device at the true target and preventingdetonation at the spurious target comprising: a contact switchresiliently biased to actuate upon application of a force greater than athreshold value and to deactivate upon release of force to less than thethreshold value; a time integration circuit operable only in response toswitch actuation, said circuit providing a firing signal when theelapsed time of switch actuation exceeds a threshold time.
 7. A fuze asdEfined in claim 6 wherein said time integration circuit comprises: apower supply; a timing capacitor; a resistor in series with said timingcapacitor, said power supply, and said sensor so that a signal from saidsensor causes charging of said timing capacitor at a selected rate; aunijunction transistor connected to said timing capacitor and reversebiased for providing a current pulse when voltage on said timingcapacitor exceeds a threshold; a storage capacitor; means connected tosaid power supply for charging said storage capacitor at a selectedrate; a silicon controlled rectifier reverse biased to be nonconducting;a network for forward biasing said silicon controlled rectifier to beconductive in response to a current pulse from the unijunctiontransistor, said silicon controlled rectifier being connected to saidstorage capacitor for discharge thereof through an external circuit. 8.A method of distinguishing a true target such as the ground and aspurious target such as a forest canopy in an ordnance fuze comprising:sensing a contact between the ordnance fuze and an object when thecontact force exceeds a threshold value; commencing a firing cycle whenthe contact is sensed; interrupting the firing cycle when the contact isbroken; and providing a firing signal when the duration of contactexceeds a time threshold.